There is a service for matching people together for masterminds - > https://mastermindjam.com/
Just to be clear, there is no requirement to use a/the service, if you have people you know that works too.
There is a lot of information around about structure and potential pitfalls as well as their solutions.
Edit: No explanation
Edit: Clarification
There was a significant delay between signing up and being matched but i am fairly certain that was due to massive demand when it first opened.
The others in my group had no such delay.
If you know other people who might be interested in doing a mastermind group with you it might be better to group with people you know.
In my case it was worth it to use the service, YMMV
Edit: dammit, double spacing
After 9 weeks, half my group quit but customer support was very responsive and my group is now 100% full again.
If you don't have the right people in your network or you don't have time to be "interviewing" a bunch of people to make up your own mastermind group, then a service like this is a no-brainer.